This invention relates to a hydraulic circuit arranged to control the amount of the fluid delivered by a variable displacement pump by the action of a dynamic pressure produced by a nozzle which is located in a bypass passage for draining the fluid under pressure into a tank and which serves to convert the static pressure into the dynamic pressure.
As for the hydraulic circuit of the kind specified, there has been generally employed a hydraulic circuit wherein a restrictor means provided with a relief valve is located in a bypass passage and the amount of the fluid delivered by a variable displacement pump is controlled by the static pressure generated upstream of the restrictor means.
In the hydraulic circuit of the above-mentioned arrangement, however, there is a risk that when the control valves are shifted to their neutral positions the static pressure upstream of the restrictor means is increased suddenly by the fluid under pressure flowing into the bypass passage thereby causing a hunting throughout the entire circuit. Therefore, a relief valve has been provided between the upstream side of the restrictor means and the circuit extending to a drain tank to deal with such a sharp sudden pressure rise. However, such a hydraulic circuit has been disadvantageous in that the cost thereof is high because of the necessity of provision of a relief valve capable of responding quickly to the above-mentioned sudden pressure rise.